Brownian and advective dynamics in microflow studied by coherent X-ray scattering experiments.

Combining microfluidics with coherent X-ray illumination offers the possibility to not only measure the structure but also the dynamics of flowing samples in a single-scattering experiment. Here, the power of this combination is demonstrated by studying the advective and Brownian dynamics of colloidal suspensions in microflow of different geometries. Using an experimental setup with a fast two-dimensional detector and performing X-ray correlation spectroscopy by calculating two-dimensional maps of the intensity auto-correlation functions, it was possible to evaluate the sample structure and furthermore to characterize the detailed flow behavior, including flow geometry, main flow directions, advective flow velocities and diffusive dynamics. By scanning a microfocused X-ray beam over a microfluidic device, the anisotropic auto-correlation functions of driven colloidal suspensions in straight, curved and constricted microchannels were mapped with the spatial resolution of the X-ray beam. This method has not only a huge potential for studying flow patterns in complex fluids but also to generally characterize anisotropic dynamics in materials.

Understanding biorelevant drug release from a novel thermoplastic capsule by considering microstructural formulation changes during hydration.

PURPOSE: To study the biorelevant drug release from novel starch-based polyvinyl alcohol capsules (S-PVA-C). The effect of the shell material is studied by considering microstructural formulation changes during hydration. METHODS: Two different self-emulsifying systems containing either fenofibrate or probucol were filled in S-PVA-C, as well as capsules of gelatin (SGC) and starch (VegaGels®). Release analysis employed a BioDis® apparatus, while disintegration was studied by texture analysis. For microstructural analysis we used small angle x-ray scattering (SAXS). RESULTS: S-PVA-C opened only partially in biorelevant media compared to completely opened SGC and VegaGels®. In case of the fenofibrate formulation, this opening mechanism caused only a short lag time, while the probucol formulation in S-PVA-C resulted in a sustained release. The latter formulation demonstrated much higher viscosity upon hydration compared to the fenofibrate system. Such a rheological effect on drug release was barely noted for SGC or VegaGels® and SAXS revealed differences in the hydrated microstructure. CONCLUSIONS: Even though S-PVA-C are highly attractive for encapsulation of rather hydrophilic formulations, some care is needed regarding an immediate release form. The type of formulation hydration must be considered for adequate selection of the capsule material.

A chaperonin as protein nanoreactor for atom-transfer radical polymerization.

The group II chaperonin thermosome (THS) from the archaea Thermoplasma acidophilum is reported as nanoreactor for atom-transfer radical polymerization (ATRP). A copper catalyst was entrapped into the THS to confine the polymerization into this protein cage. THS possesses pores that are wide enough to release polymers into solution. The nanoreactor favorably influenced the polymerization of N-isopropyl acrylamide and poly(ethylene glycol)methylether acrylate. Narrowly dispersed polymers with polydispersity indices (PDIs) down to 1.06 were obtained in the protein nanoreactor, while control reactions with a globular protein-catalyst conjugate only yielded polymers with PDIs above 1.84.

Monofunctionalized gold nanoparticles stabilized by a single dendrimer form dumbbell structures upon homocoupling.

The assembly of dumbbell structures as organic-inorganic hybrid materials is presented. Gold nanoparticles (NPs) with a mean diameter of 1.3 nm were synthesized in very good yields using a stabilizing dendrimer based on benzylic thioether subunits. The extended dendritic ligand covers the NP surface and contains a peripheral protected acetylene, providing coated and monofunctionalized NPs. These NPs themselves can be considered as large molecules, and thus, applying a wet-chemical deprotection/oxidative acetylene coupling protocol exclusively provides dimers of NPs interlinked by a diethynyl bridge. The concept not only enables access to novel organic/inorganic hybrid architectures but also promises new approaches in labeling technology.

Gold nanoparticles stabilized by thioether dendrimers.

Ligand-stabilized gold nanoparticles (Au NPs) are promising materials for nanotechnology with applications in electronics, catalysis, and sensors. These applications depend on the ability to synthesize stable and monodisperse NPs. Herein, the design and synthesis of two series of dendritic thioether ligands and their ability to stabilize Au NPs is presented. The dendrimers have 1,3,5-trisubstituted benzene branching units bridged by either meta-xylene or ethylene moieties. A comparison between the two ligands shows how both size control and the stability of the NPs are influenced by the nature of the ligand-NP wrapping interaction. The meta-xylene-bridged ligands provided NPs with a narrow size distribution centered around a diameter of 1.2 nm, whereas the NPs formed with ethylene-bridged dendrimers lack long-term stability with NP aggregation detected by UV/Vis spectroscopy and transmission electron microscopy. The bulkier tert-butyl-functionalized meta-xylene bridges form larger ligand shells that inhibit further growth of the NPs and thus provide a simple route to stable and monodisperse Au NPs that may find use as functional components in nanoelectronic devices.